1. Field of the Invention
This invention pertains to an automatic bill accepting apparatus and a method of detecting a skewed bill (i.e. bank note) that is inserted to the apparatus. The apparatus is typically used in an automatic commodity vending machine, an automatic ticket issuing machine, or an automatic money exchanging machine.
2. Description of the Prior Art
A conventional automatic bill accepting apparatus used in an automatic commodity vending machine etc. has a bill inlet port, a bill transport path and a bill transport mechanism. The bill inserted through the inlet port is transported in the transport path in a predetermined direction. The bill accepting apparatus normally has a bill identification and verification means, typically of a photo-electronic type, that identifies denomination of the bill and verifies its genuineness.
One of the serious problems pertaining to a bill accepting apparatus is skewing or jamming of a bill. Such skewing or jamming problem occurs when the bill is inserted to the inlet port in a skewed state or bill transport rollers in a bill transport mechanism apply uneven pressures onto the bill. Naturally, the bill will not be correctly identified or verified when it is skewed or jammed in the apparatus.
The Japanese laid-open patent application, laid-open no. 4-264997, dated Sep. 21, 1992, discloses an automatic bill accepting apparatus having a pair of first and second photo-electronic bill inlet sensors disposed on an imaginary line that is orthogonal to the bill transport direction in the bill transport path and close to the bill inlet port. These two sensors are disposed close to respective side ends of the bill transport path. A photo-electronic bill recognition sensor, which is the third sensor, is disposed further inside of the bill transport path. A bill is detected by the first and/or the second sensor as soon as the bill is inserted to the bill inlet port. The bill is identified and verified by the third sensor after it has been advanced in the bill transport path.
The Japanese patent publication further discloses a method of detecting a skewed bill. According to the method, an elapsed time after the third sensor detects the leading edge of the bill until either the first sensor or the second sensor first detects the trailing edge of the bill is measured. If the bill is skewed, the measured elapsed time will be smaller than the comparable elapsed time when the bill is being transported without a skew. The measured elapsed time is compared with a predetermined value, and if the measured time is smaller than the predetermined value, it is determined that the bill is skewed and the bill transport rollers are driven in reverse to return the bill.
In the above mentioned conventional method of detecting a skewed bill by measuring the elapsed time from the instance the leading edge of the bill reaches the bill recognition sensor until its trailing edge reaches one of the bill inlet sensors, any fluctuation of power source voltage or change of ambient temperature, or aging of the bill transport mechanism, which causes a change of frictional loss in the transport mechanism, tends to cause variation of bill transport speed. This adversely affects the accuracy of the measurement of the elapsed time. Furthermore, by the time the trailing edge of the bill reaches one of the bill inlet sensors, the bill may have already jammed in the bill transport path and, therefore, it may be too late to return the bill by driving the bill transport rollers in reverse.